Sorry to hear yet another tale about an Evri non delivery with such an unhappy outcome. I do hope that your tank may still turn up. If you do decide to get a new tank made I have heard of a tank maker near to me here in Wales. From their website they say that they have been in business from the early 70's and offer a wide range of alloy products. I couldn't find a Silk in their amazing picture gallery of previous tanks made in situ.
Their website is
https://tabclassics.comSince they are not far from me I am prepared to take my Silk tank along for them to measure up if they would be happy with that. I wouldn't be able to leave it there though. The one caveat is that my Silk is made from an earlier Silk Scott frame and I don't know if there is any difference with the tank mountings.
Good luck with coming up with a solution and I hope that Evri are going to pay for it.